Non-linear resistive elements generally called a varistor show a characteristic of a resistance value thereof varying with a voltage applied thereto, i.e., have a non-linear voltage-current characteristic such that the element has a high resistance value to show an insulating characteristic when a normal voltage is applied thereto, while having a low resistance value when an abnormal high voltage is applied thereto. Among non-linear resistive elements having such a characteristic, a non-linear resistive element including zinc oxides as a primary component has an excellent non-linear voltage-current characteristic.
Such a non-linear resistive element is manufactured by the following method, for example. That is, a large quantity of zinc oxide as a primary component and a very small quantity of basic additive such as bismuth oxide, antimony oxide, cobalt oxide or manganese oxide to develop a non-linear voltage-current characteristic are wet-mixed, and slurry as a result of the wet-mixing is granulated by spray drying. The granulated powder is shaped into a cylindrical-form compact (green body), and it is sintered to be a ceramic sintered body. Then, a glass material is applied and glazed onto the collaring of the ceramic sintered body to form insulated layers for flashover prevention, to which heat treatment is applied as needed, and electrodes are further formed at upper and lower end faces of the ceramic sintered body by aluminum thermal spraying or the like (see Patent Document 1, for example).